iencode64: Encode/decode 64-bit integer numbers as short strings

In s-u/morton: Functions for Handling Morton Code

Description

iencode64 encodes up to 64-bit intgers numbers into a concise ASCII string representation. It uses the same characters as base64 encoding, but in strictly lexicographically ascending order and encodes only as many characters as are necessary to include the most significant bit set to 1.

Usage

iencode64(x, min.length = 1L)
idecode64(x)

Arguments

x	iencode64: numeric vector of values to encode. Reals are truncated to 64-bit unsigned integer values. idecode64: character vector of encoded values.
min.length	integer, minimal length of the encoded strings.

Details

Although the encoding is closely related to base64 encoding, it is not the same, because it encodes only as many 6-bit groups as are needed and the order of the characters is different. However, due to the design that characters in the encoding table are in lexicographically ascending order, the lexicographical order of the strings (as long as they are all left-padded to the same length) is equal to the order of the encoded values.

Numeric values are truncated to 64-bit unsigned integers before encoding.

Decoding of a value stops if a character outside of the b64 alphabet (alphanumeric, plus and slash) is encountered. If the value overflows (more than 64 bits are encoded) the behavior is undefined (currently the code discards MSB that are beyond 64-bit).

Value

iencode64: character vector of encoded values

idecode64: numeric vector of decoded values (integers)

Note

Missing values (NA) are preserved.

Author(s)

Simon Urbanek

Examples

  iencode64(1234)

  idecode64("ABC")

  x = floor(runif(100, 0, 2^32))
  iencode64(x[1:10])
  stopifnot(x == idecode64(iencode64(x)))

s-u/morton documentation built on May 28, 2019, 10:48 a.m.